For golfers, flight distance of a ball is one of the important factors when selecting a golf club. Therefore, hitherto, in order to extend the flight distance of the ball, various improvements have been made with regard to shapes and materials of elements forming a golf club.
However, in recent years, in order to suppress an excessive flight distance so as to increase fairness of game, a repulsion performance of a face, club length, and inertia moment of a head are regulated by rules. Thus, improvement of the flight distance is getting more difficult.
Under such a situation, in consideration with the fact that initial velocity of the ball largely influences the flight distance, it is proposed to extend the club length close to an upper limit regulated by the rules so as to increase head speed of the club (for example, refer to Patent Literature 1).